Subchunk (/) Data Format
Byte Order
Subchunk data is stored in Little Endian byte order.
Parsing The Subchunk
NOTE: Bedrock subchunks are only saved to disk if they have changed since world generation.
| Name | Size (in bytes) | Description |
|---|---|---|
| Version | 1 | The version of this subchunk. |
If Version is 8 and 9
| Name | Size (in bytes) | Description |
|---|---|---|
| Block Layer Count | 1 | The number of block layers this subchunk has. |
| Y-Index | 1 | The Subchunk Y Position (ranges from -4 to 19). (Only exists if Version is 9) |
Now loop the next section Block Layer Count times until you have parsed all block layers.
| Name | Size (in bits) | Description |
|---|---|---|
| Palette Type | 1 | The type of this palette (0 = Persistence, 1 = Runtime) |
| Bits Per Word | 7 | How many bits are used for each word. |
If Palette Type is 0
| Name | Size (in bytes) | Description |
|---|---|---|
| Layer Indices | ceil(4096[1] ÷ Blocks Per Word[2]) × 4 | Stored as Blocks Per Word indices, with each unsigned 32-bit integer containing multiple indices, each occupying Bits Per Word bits. The indices are packed and stored in YZX order (Y increments first). |
| NBT Palette Compound Count | 4 | The number of NBT compounds to parse |
| NBT Palette Compounds | Variable | Multiple NBT compounds of individual blocks of the palette used in this subchunk |
If Palette Type is 1 (Might not be used in practice)
| Name | Size (in bytes) | Description |
|---|---|---|
| Layer Indices | ceil(4096[1] ÷ Blocks Per Word[2]) × 4 | Stored as Blocks Per Word indices, with each unsigned 32-bit integer containing multiple indices, each occupying Bits Per Word bits. The indices are packed and stored in YZX order (Y increments first). |
| NBT Palette Compound Count | 1 Signed VarInt (ZigZag) | The number of NBT compounds to parse |
| NBT Palette Compounds | Variable | Multiple NBT compounds of individual blocks of the palette used in this subchunk |
If Version is 0 or between 2 and 7
NOTE: Second block layer for this version uses LegacyBlockExtraData (4) key instead, rather then being stored with the subchunk like in newer versions of the format.
| Name | Size (in bytes) | Description |
|---|---|---|
| Block IDs | 4096 | 8 bits per block. All the block ids for this chunk stored in YZX order (Y increments first) |
| Block Data | 2048 | 4 bits per block. All the data values for the blocks in this chunk stored in YZX order (Y increments first) |
| Skylight | 2048 | 4 bits per block. May be omitted. All the skylight data for this chunk stored in YZX order (Y increments first) |
| Blocklight | 2048 | 4 bits per block. May be omitted. All the blocklight data for this chunk stored in YZX order (Y increments first) |
Notes
- In some languages you may need to write this as
4096.0instead of just4096for the correct output. - Blocks Per Word = floor(32 ÷ Bits Per Word)
Contributors
BJTMastermind